The invention relates generally to the field of magnetic bubble technology (MBT) and more particularly to logic arrangements utilizing the capabilities of single wall magnetic domain devices.
The continuing evolution of MBT has now reached the point where large scale application to various data processing tasks is practicable. Current interest in MBT is due primarily to the prospect of extremely high bit-packing density, low power consumption and reliability for low cost mass memories. Briefly, MBT involves the creation and propagation of single wall magnetic domains in specially prepared magnetic materials. The application of a static uniform magnetic bias field orthogonal to a sheet of magnetic material having suitable uniaxial anisotropy causes the normally serpentine pattern of magnetic domains to shrink into short cylindrical configurations called bubbles whose common polarity is opposite that of the bias field. The bubbles repel each other and can be moved or propagated by a magnetic field in the plane of the sheet.
Many schemes now exist for propagating bubbles along predetermined channels. One propagation system includes permaloy circuit elements shaped like military service stripes or "chevrons" spaced end-to-end in a thin layer over a sheet of magnetic material. The drive or propagation field is continuously rotating in the plane of the sheet causing each chevron to act as a small magnet whose poles are constantly changing. As the drive field rotates, a bubble under one of the chevrons is moved along the chevron channel from point to point in accordance with its magnetic attraction to the nearest attracting temporary pole of the circuit elements. This system is among those referred to as "field-access" as distinguished from other systems employing loops of conductors disposed over a magnetic sheet.
The use of MBT in data processing stems from the fact that the bubbles can be propagated through their channels at a precisely determined rate so that uniform data streams of bubbles are possible in which the presence or absence of a bubble indicates a binary 1 or 0. The use of MBT for performing logic operations is based on the fact that close magnetic bubbles tend to repel each other. Thus, if alternate paths with varying degrees of preference are built into the chevron circuit, the direction which a bubble on one channel ultimately takes may be influenced by the presence or absence of a bubble on another closely spaced channel.
Besides the inherent capability of performing logic with magnetic domains, one other aspect of MBT has given impetus to logic development. MBT was originally envisioned as a mass memory, but the most difficult problem has been encountered in readout. Optional devices utilizing the Faraday effect and magneto-resistive devices have been used, but are not entirely satisfactory. Therefore, it is important to minimize readout to the extent possible by incorporating logic in the memory so that the magnetic bubbles representing information can be logically manipulated before readout is necessary, thus increasing the quality or informational content of each bit of readout.
In the copending U.S. patent application, Ser. No. 283,267, filed Aug. 24, 1972, by Robert C. Minnick et al, entitled "Magnetic Bubble Logic Family", the concept of conservative versus non-conservative bubble logic gates is discussed and all of the possible three input -- three output or 3--3 conservative bubble logic gate functions are determined. A substantial portion of the disclosure in the copending application has been published in the Proceedings of the Sept. 19, 1972, Wescon conference in a paper entitled "Magnetic Bubble Logic" by R. C. Minnick et al.
These disclosures describe simple realizations for each of 31 distinct classes of logic functions produced by 3--3 circuits and introduce a special symbology for bubble logic circuits. That symbology as well as the complete list of distinct logic functions and specific realizations is incorporated by reference into this application. The symbology used in the present application is completely consistent with that used in the above disclosures. Accordingly, the avoid undue repetition the development and definition of the symbology and logic circuits already described will be omitted from this application in the interest of emphasizing the specific new circuits contained herein.
Magnetic bubble flip-flop circuits have been described before. For example, circuits using a circulating or "idling" bubble are shown in the following applications: "Propagation of Cylindrical Magnetic Domains in Orthoferrites", Perneski, IEEE Transactions on Magnetics, September 1969, p. 554; "Resident-Bubble Cellular Logic Using Magnetic Domains", Garey, IEEE Transactions on Computers, April 1972, p. 392; "Field-Access Bubble-to-Bubble Logic Operations", Carlson et al, Intermag Conference Proceedings, 1972, and U.S. Pat. No. 3,638,208 to Chow entitled "Magnetic Domain Logic Circuit". U.S. Pat. No. 3,638,208 also discloses a toggle or trigger flip-flop. A magnetic bubble write decoder is shown in "A Self-Contained Magnetic Bubble Domain Memory Chip", Chang, IEEE Transactions on Magnetics, volumn MAG-8, No. 2, June 1972, p. 214.